Analog to Digital Converters (ADC) are well-known circuitries and widely used in many electronic devices. They convert an analog input voltage into a digital output signal as a number of bits. Normally there is a linear correlation between input voltage and digital output value. Important performance data is the resolution normally characterized as number of output bits and the conversion speed of the converter which is measured in samples per second.
An other very important criteria for the practical application is the ability to implement the ADC into an integrated circuit at low cost. On such a chip analog circuitries with high accuracy are not easily implementable at low cost. Furthermore—compared to digital circutries—the nearly automatic shrinking with each new chip generation is not feasible.
Because of this ADCs using the Delta-Sigma principle were widely spread during the recent years. These ADCs normally only use a 1-bit ADC and reach higher resolution by oversampling of the input signal with a following digital filtering. So the analog circuitry is small and furthermore some shortcomings of the analog circuitry are not influencing the quality of the ADC.
Disadvantage of a Delta-Sigma type ADC is the necessary oversampling. This means that the data rate of the converter is far below the sample rate. Because of this fast ADCs with effective data rates of more than 10 Megasamples/s are not feasible as delta-sigma ADCs. Here up to now expensive Flash type converters are used. This kind of ADC suffer from the disadvantage that the effort for the circuitry is increasing exponentially with the number of output bits.